The field of the present invention relates generally to broadband distribution equipment for use with a telephone communication system involving a coaxial drop cable and, more specifically, to a method and apparatus for providing continuous power and bandwidth transmission downstream of a subscriber while a coaxial, multiple port xe2x80x9ctapxe2x80x9d is being serviced.
Multiple port taps are known in cable television networks for tapping off a main signal feeding coaxial cable to provide a signal to a respective number of customers. These taps can include one port, two ports, four ports or eight ports. In a typical cable television distribution system, a plurality of these multiple port tap devices are connected as required along the length of the main signal and power feeding line for tapping and distributing television signals to a plurality of the customers. Typically, the main signal feeding cable is passed into the multiple port tap at an input port along the side of the tap, and the main signal feeding cable is continued from an output port on the opposite side of the tap. The feeding cable that extends from the output port of one tap extends into the input port of the next, downstream multiple port tap. As more customers are added to conventional systems, it can become necessary for the line to be lengthened, spliced, etc., and/or for the level of power of the signal being conducted by the main cable to be increased. It is also known to have the main distribution cable conduct both the television or RF signal along with the AC power necessary to energize the electronic circuitry of any active devices in the network.
Conventional multiple port taps require the cover plate to be removed when any type of service is performed. Removal of the cover plate results in an interruption of the signal and power to downstream subscribers. Typical service includes, but is not limited to diagnostic testing, substituting a new cover plate and circuit board for a defective one, repairing a particular output tap connector, and changing the impedance across the tap. A proper impedance level across a tap must be maintained so that an appropriate signal level is provided to the subscribers connected to the tap and downstream of the tap. An appropriate impedance level is also required so that an appropriate downstream power level is maintained for activating devices such as amplifiers. Without appropriate signal and power levels being transmitted from a tap, the service to customers directly fed by the tap and those downstream of the tap will be interrupted until the servicing of the tap under repair or conversion is completed.
Many attempts have been made to overcome this problem. These include providing a conventional tap with a built-in, manually closeable switching mechanism that, for example, after a tap plate is removed, reconnects the RF signal and AC power to the downstream taps. However, the manually closable switch does not provide continuous, uninterrupted service of the RF signal and AC power to the downstream taps and subscribers. Instead, the signal and power are interrupted until the switching mechanism can be activated. U.S. Pat. No. 5,677,578 to Tang discloses a multi-port tap intended to provide continuous, uninterrupted RF signal and AC power to downstream taps and subscribers. The multi-port tap of Tang uses a shunt printed circuit board having a conductive path for RF signal and AC power. The shunt board is biased into contact with the main feed line as the tap plate is removed. A major drawback to the multi-port tap of Tang is its inability to attenuate the RF signal in order to accurately compensate for the signal loss due to the removal of the face plate. Because the signal is not attenuated to the value of the face plate, service to some downstream providers will be interrupted while the face plate is removed. Also, the multi-port tap of Tang and the prior art taps do not include a service port that allows for diagnostic procedures to be performed or attenuation values to be changed without removing the tap plate.
There is a need for a multiple port tap for use with a communication system that overcomes the drawbacks of the prior art. In particular, there is a need for a multiple port tap that while being repaired provides continuous, uninterrupted RF signal and AC power to downstream taps and subscribers for the duration of the service or repair. There is also a need for such a multiple port tap that includes a variable attenuator for maintaining the impedance across the tap at a predetermined level equivalent to the value of the tap in question. Further, a multiple port trap including a diagnostic and attenuation adjustment service port is also needed so that the tap can be converted to a higher or lower attenuation factors without any interruption of RF signal and AC power to down the multiple port taps and subscribers.
An object of the invention is to provide a new and improved multiple port tap. Another object of the invention is to provide a multiple port tap that ensures uninterrupted, attenuated RF signal and AC power to downstream multiple port taps, whenever a tap plate of an upstream multiple port tap is removed. It is a further object of the present invention to provide such a tap including a signal and power bypass having a variable attenuator for changing the impedance in the bypass.
One embodiment of a multiple port tap according to the present invention includes a tap housing, means for receiving a main signal from an upstream element and means for outputting the main signal to a downstream element. The tap also includes circuitry that couples the signal receiving means to the signal outputting means. The tap circuitry used in the tap includes a signal attenuator for maintaining a predetermined RF signal and AC power level across the tap. A housing cover plate is positioned on the housing for covering the main opening to the housing. The cover plate includes at least one subscriber connection port operatively coupled to the circuitry for delivering a signal to a subscriber. The tap further includes a signal and power bypass having a variable attenuator for coupling to the signal receiving means and signal outputting means. The bypass provides a signal and power pathway around the circuitry so that uninterrupted service is provided to the downstream element while the tap is being serviced.
The bypass tap can either be completely positioned in the tap housing or it can be an external bypass secured to the housing through bypass ports. An external signal bypass according to the present invention comprises a first signal receiving end for coupling with the main signal input connector of the multiple port tap, a second signal receiving end for coupling with the main signal output connector of the multiple port tap, and a variable impedance attenuator positioned between the first and second signal receiving ends for delivering a predetermined signal and power to the main signal output connector of the multiple port tap when the tap is being serviced.
A second embodiment of the multiple port tap according to the present invention comprises a tap housing and cover plate removably secured to the tap housing. The tap also comprises a feeder signal input port for receiving an upstream line carrying a main feeder signal, a feeder signal output port for allowing passage of a downstream line carrying the main feeder signal to a downstream element, and a signal connection port positioned between the signal input port and the signal output port for receiving an end of each of the lines. An attenuating member is removably positioned within the connection port for establishing a RF signal and AC power flow path between the ends of the lines. The attenuating member has a preset impedance value for providing a feeder signal having a predetermined strength to a downstream element. The attenuating member according to this embodiment allows for the impedance of the tap to be quickly and easily changed without having to remove the cover plate from the housing. As discussed below, this embodiment can be used with either an internal or an external signal and power bypass.
A third embodiment of a tap for use in a coaxial communication system according to the present invention includes a main tap housing having an opening, an input signal connector operatively associated with an input port for receiving a main feeder signal, and an output signal connector operatively associated with an output port for delivering the main feeder signal to a downstream element. A main housing cover is removably secured to the main tap housing for closing the housing opening. The tap also includes circuitry for delivering the main feeder signal from the input signal connector to the output signal connector. Moreover, an externally accessible service port is operatively coupled to the circuitry so that a diagnostic analysis of the active tap can be performed while the main housing cover is secured to the main tap housing. The externally accessible service port can be used with any of the other tap embodiments according to the present invention for performing service on a multiple port tap without removing its cover plate.
The present invention also includes a method of providing a continuous, attenuated feeder signal across a tap in a coaxial communication system while the tap is serviced. The method comprises the steps of providing a tap including a housing having an open top, a cover plate removably secured to the housing for closing the open top, an input signal connection member for receiving the feeder signal, an output signal connection member for outputting the feeder signal to a downstream element and a printed circuit board for carrying the feeder signal between the signal connection members. The method also includes the steps of providing a signal bypass having first and second ends for coupling to a respective one of the signal connection members. The signal bypass also includes a variable attenuator positioned between its first and second ends. The method further includes the steps of coupling the first end of the signal bypass to the input signal connection member, coupling the second end of the signal bypass to the output signal connection member, and activating the signal bypass. Before the bypass is activated, the variable attenuator must be set at a predetermined impedance level. After the bypass has been activated, or as it is being activated, the circuit board is disconnected from the signal connection members so that the feeder signal flows from the input signal connection member to the output signal connection member through the signal bypass.